The present invention relates to a method of guiding a missile towards a moving target and also relates to an arrangement in a missile for guiding the missile towards a moving target.
Several earlier methods of guiding a missile towards a moving target already exist. A central principle is that the missile has access to information on the position and velocity vector of the target and manoeuvres which lead towards a collision point, the missile velocity vector at all times pointing ahead of the target. In proportional navigation it is assumed that the target is all the time moving in the same direction and at a constant speed, the information being used so that rotation of the line of sight becomes zero; the missile manoeuvres 3-4 times faster than the rotation of the line of sight between the missile and the target. This guidance can be modified. For example, account can be taken of measured target acceleration across the line of sight.
GB, 2 279 444,A shows a system for guiding missiles. The system is intended to guide the missile along a straight trajectory when it is nearing its target, consequently preventing the missile from being exposed to excessively high g-forces. The system comprises means of tracking the target and continuously predicting its ballistic trajectory and tangents thereto. The future behaviour of the target is predicted by using the current condition and a mathematical model of the state of the atmosphere and the gravitation. The system furthermore has means of continuously determining the relative position, speed and acceleration of the missile and the target, and means of calculating an interception time therefrom. In addition the system has means of guidance for guiding the missile on to and along a tangent to the predicted ballistic trajectory ahead of the target corresponding to the interception time.
An object of the present invention is to eliminate or at least reduce the limitations that are associated with earlier known systems outlined above, due to the use, if any, of a highly simplified assumption as to the movement of the target.
Preferred methods and embodiments have any or some of the characteristics specified in the subordinate claims for each respective claim category.
The method and the arrangement according to the invention have various advantages. One important advantage is that the method and the arrangement according to the invention are designed for guiding towards manoeuvrable targets, the further movement of which is unpredictable and which in many applications have an objective of their own, opposed to that of the missile, namely to avoid being hit. The method and the arrangement according to the invention can cope with this guidance towards manoeuvrable targets in that, instead of homing at a tangent (lead point guidance) the missile homes in towards the predicted point of interception, which is calculated on the basis of a speculation as to what manoeuvres the target can be expected to perform up to the time of impact. Any knowledge of the type of target can contribute to a prediction of the target behaviour and hence to an estimation of the point of interception.
Another advantage is that improved kinematic performance is obtained due to the lesser resistance induced. This is explained by the fact that the missile velocity vector varies at a slower rate and is not directly affected by changes in the trajectory of the target.
A further advantage is that the missile manages to hit the target within a greater area of coincidence despite more complicated target behaviour than is feasible with previously known methods of missile guidance.